Welding method, welding device, welded joint, and welded structure

ABSTRACT

A welding method is disclosed for butt welding a first base material  1  and a second base material  2  with each other. To also permit stable and efficient formation of a bead in the form of a fillet weld on a back side of a groove by conducting arc welding from the side of the groove without arranging a bead beforehand on the back side of the groove, the first member  1,  on which a root face  1   a  and a single groove face  1   b  have been formed, is brought at its root face  1   a  into contact with a flat surface  2   a  of the second base material  2.  A welding wire  6  is arranged facing on the groove formed by the contact between the first base material  1  and the second base material  2.  The first base material  1  and the second material  2  are caused to fuse at an area of contact between them by an arc from the welding wire  6.  A melt, which has been formed by the fusion at the area of contact and the like, is forced out to the back side of the groove to form a bead B 4  in the form of a fillet weld on the back side of the groove.

TECHNICAL FIELD

This invention relates to a welding method to be conducted by arranginga single groove face, a welding apparatus useful in the welding method,and a welded joint and welded structure available by the method.

BACKGROUND ART

In a variety of welded structures such as steel skeleton constructionsof buildings, bridges, industrial equipment and construction machinery,“T” joints are adopted as welded joints in many instances. In general, a“T” joint is formed by bringing a single groove face of one of membersinto abutment against a surface of the other member to arrange thesemembers in a “T” pattern and forming a bead in a groove, which has beenformed at an area of contact between the surface of the above-mentionedother member and the above-mentioned one member, to join these memberstogether. As known examples of this type, there are the welding methodsdisclosed in JP-A-08332567 and JP-A-06023544. The former conventionaltechnique requires advance arrangement of a bead on the back side of agroove, which is formed at an area of contact between two members, toavoid burn-through of a groove root portion. The latter conventionaltechnique, on the other hand, requires advance arrangement of a bead onthe back of a groove, which is formed at an area of contact between twomembers, to prevent the weld metal from punching through or any partfrom remaining undeposited.

As a control method for making a center of a welding torch trace a weldline upon conducting automated welding, an arc sensor is widely employedto make use of electrical changes associated with changes in arc lengthand wire extension when the welding torch is caused to weave in thedirection of the width of a groove. As conventional art of this sortprimarily for an offset in the direction of the width of a groove, it isknown, as disclosed in JP-B-53011502, to compare the magnitude of anintegral of welding currents obtained at left ends of weaving with thatof an integral of welding currents obtained at right ends of the weavingand then to correct the welding torch leftward or rightward on the basisof a signal representative of the comparison to trace a weld line.

To prevent the burn-through of a groove root portion at an area ofcontact between one of members, said one member having a single grooveface, and the other member against which the single groove surface isbrought into abutment, the above-mentioned conventional techniqueincludes advance arrangement of a bead at the area of contact on a sideopposite to the welded side. Depending on the shape of a welded jointstructure or welded structure, however, it may be difficult, from thestandpoint of actually performing welding, to arrange a bead beforehandon the back side of a groove as in the above-mentioned conventionaltechnique.

When performing automated welding, an arc sensor is widely employed asin the above-mentioned conventional technique. Conventional arc sensingmethods, however, have difficulty in tracing a weld line because theyare not designed to be applicable to such a welding method that by arcwelding from the side of a groove, a bead is formed on the back side.

It is also difficult to trace a weld line when a move or deformationoccurs in a groove in the direction of the width of the groove or in thedirection of a distance to a tip of a welding wire due to restraintconditions for a first base material and second base material or athermal distortion or the like upon welding.

With the foregoing in view, work-related limitations are considered tobe eliminated provided that a bead in the form of a fillet weld can bestably formed on the back side of a groove by arc welding from the sideof the groove without arranging any bead beforehand on the back side ofthe groove.

The present invention has been completed in view of such backgroundcircumstances, and its objects are to provide a welding method forpermitting stable and efficient formation of a bead in the form of afillet weld on a back side of a groove by arc welding from the side ofthe groove without arranging a bead beforehand on the back side of thegroove, a welding apparatus useful for the welding method, and a weldedjoint and welded structure fabricated by the welding method.

DISCLOSURE OF THE INVENTION

To achieve the above-described objects, the present invention isconstituted as will be described in the following aspects.

Described specifically, a first aspect is characterized in that in awelding method for butt welding a first base material and a second basematerial with each other, the welding method comprises bringing thefirst base material, on an end portion of which a root face and a singlegroove face have been formed, into contact at the root face thereof witha flat surface of the second base material, arranging a welding wire toface on a groove formed by the contact between the first base materialand the second base material, causing the first base material and thesecond material to fuse at an area of contact therebetween by an arcfrom the welding wire, and forcing a melt, which has been formed by thefusion, out to a back side of the groove to form a bead on the back sideof the groove.

According to the first aspect, a difference in thermal capacity betweenthe first base material provided with the single groove face and thesecond base material having the flat surface and fusion of the weldingwire make it possible to achieve welding in the groove and also tostably deposit a bead in the form of a fillet weld on the back side ofthe first base material, said back side being on a side opposite to theside of the groove. Described specifically, the bead in the form of thefillet weld can also be formed by causing a greater portion of the arcto generate on the side of the second material the thermal capacity ofwhich is greater, causing the first base material, the thermal capacityof which is smaller, to fuse to such an extent that the first basematerial is not punched through, and forcing out the melt of the weldingwire to the back side of the first base material, said back side beingon the side opposite to the side of the groove, while filling up thegroove with the melt of the welding wire. As no work is needed for thearrangement of an auxiliary bead, a backing strip and the like, theworkability during welding can be improved, and moreover, themanufacturing cost can be lowered.

A second aspect is characterized in that in a welding method for buttwelding a first base material and a second base material with eachother, the welding method comprises positioning a center axis of an arcfrom a welding wire at an aimed point, which is located either at aposition of contact between a single groove face formed on the firstbase material and a flat surface of the second base material or at aposition adjacent and not farther than the position of contact,obliquely irradiating the arc at a predetermined inclination onto theflat surface of the second base material in a direction passing throughthe aimed point such that the first base material and the second basematerial are caused to fuse at an area of contact therebetween, andforcing a melt, which has been formed by the fusion, out to a back sideof the groove to form a bead on the back side of the groove.

According to the second aspect, the bead can be stably formed becausethe stability in the feeding of a voltage and current to the area ofcontact can be enhanced.

A third aspect is characterized in that in the second aspect, thewelding wire is caused to weave with a predetermined oscillation widthwithin the groove while maintaining the predetermined inclination.

A fourth aspect is characterized in that in the second aspect, thewelding wire is caused to weave with a predetermined oscillation widthwith a center of weaving set at a predetermined point on thepredetermined inclination within the groove.

According to the third or fourth aspect, stable welding is feasible bythe weaving operation of the welding wire.

A fifth aspect is characterized in that in the third or fourth aspect,while the welding wire is weaving, a change in welding voltage orwelding current during a time after the arc moves past the predeterminedposition until the arc moves toward the first base material and returnsback to the position of contact is detected based on a time at which thearc passes through the position of contact, and the welding wire ismoved in a direction of a width of the groove on a basis of thethus-detected change such that the center of the weaving always remainsat an appropriate position relative to the groove.

According to the fifth aspect, even if a move or deformation takes placein the groove in the direction of the width of the groove due torestraint conditions for the first base material and the second basematerial and/or a thermal distortion during welding, the welding can beappropriately corrected to trace a weld line in the groove by moving thewelding wire. This makes it possible to more accurately force out themelt to the back side of the groove and hence, to also form a bead inthe form of a fillet weld.

A sixth aspect is characterized in that in the third or fourth aspect,while the welding wire is weaving, a change in welding voltage orwelding current during a time after the arc moves past the predeterminedposition until the arc moves toward the first base material and returnsback to the position of contact is detected based on a time at which thearc passes through the position of contact, and a tip of the weldingwire is moved toward or away from the position of contact on a basis ofthe thus-detected change such that the center of weaving always remainsat an appropriate position relative to the groove.

According to the sixth aspect, even if a relative movement takes placebetween the groove and a tip of the welding wire due to restraintconditions for the first base material and the second base materialand/or a thermal distortion or the like during welding and theirpositional relation is changed from their preset positional relation,the welding can be appropriately corrected to trace a weld line in thegroove by moving the tip of the welding wire toward or away from thegroove. This makes it possible to more accurately force out the melt tothe back side of the groove and hence, to also form a bead in the formof a good fillet weld.

A seventh aspect is characterized in that in the first or second aspect,the bead formed on the back side of the groove is a weld bead in a formof a fillet weld.

According to the seventh aspect, a bead in the form of a fillet weld canbe stably formed.

An eighth aspect is characterized in that in the first or second aspect,a current for generating the arc is a direct current.

A ninth aspect is characterized in that in the first or second aspect, acurrent for generating the arc is a current obtained by superimposing adirect current and a pulse current on each other.

A tenth aspect is characterized in that in the first or second aspect, acurrent for generating the arc is a sinusoidal current.

According to the ninth or tenth aspect, the directivity of the arc isimproved and, even if a slight offset occurs between the welding wireand the aimed point for a certain reason, the arc is not disturbed toomuch and the amount of a melt to be forced out to the side opposite tothe groove is stabilized. It is, therefore, possible to form a bead inthe form of a fillet weld and to perform stable welding.

An eleventh aspect is characterized in that in a welded “T” joint with afirst base material and a second base material butt welded with eachother, the first base material and the second base material have beenjoined together at an area of contact between a flat surface of thesecond base material and the first base material, on which a root facepositioned in contact with the flat surface and a single groove face areformed, by causing the first base material and the second base materialto fuse at the area of contact with an arc from a welding wirepositioned facing on a groove formed by the single groove face and theflat surface and forcing a melt, which was formed by the fusion, out toa back side of the groove to form a bead in a form of a fillet weld.

A twelfth aspect is characterized in that in a butt-welded “T” joint offlat plates with a first base material and a second base material buttwelded with each other, the first base material and the second basematerial have been joined together at an area of contact between an endsurface of the second base material and the first base material, onwhich a root face positioned in contact with the end surface and asingle groove face are formed, by causing the first base material andthe second base material to fuse at the area of contact with an arc froma welding wire positioned facing on the groove and forcing a melt, whichwas formed by the fusion, out to a back side opposite to a side of thegroove to form a bead in a form of a fillet weld.

A thirteenth aspect is characterized in that in a box-shaped, weldedstructure formed by butt welding a plurality of base materials made ofplates, each two base materials butt welded with each other have beenjoined together at an area of contact between a flat surface of one ofthe two base materials and the other base material, on which a root facepositioned in contact with the flat surface and a single groove face areformed, by causing the base materials to fuse at the area of contactwith an arc from a welding wire positioned facing on a groove formed bythe single groove face and the flat surface and forcing a melt, whichwas formed by the fusion, out to a back side of the one base material,said back side being on a side opposite to a side of the groove, to forma bead in a form of a fillet weld.

According to the eleventh to thirteenth aspects, it is possible toprovide a welded joint or box-shaped structure which is low inmanufacturing cost and permits a reduction in manufacturing time.

A fourteenth aspect is characterized in that in a welding apparatus forbutt welding a first base material and a second base material with eachother, the welding apparatus comprises a welding wire to be introducedinto a groove formed at an area of contact between the first basematerial and the second material, a control device for controlling aposition of the welding wire, a welding power source for feeding weldingelectric power to the area of contact, and control means for outputtinga command to the control device such that the welding wire is movedtoward the second base material when an actual voltage fed from thewelding power source to the area of contact has exceeded a first presetvoltage level set in advance and the welding wire is moved toward thefirst base material when an actual current fed from the welding powersource to the area of contact has exceeded a preset current level set inadvance or the actual voltage has fallen below a second preset voltagelevel set in advance.

According to the fourteenth aspect, while performing arc welding of thefirst base material and the second base material from one side, thecenter axis of an arc can be accurately position-controlled at apredetermined inclination relative to the second base material so that abead in the form of a fillet weld can be stably formed on the back sideof the groove side.

A fifteenth aspect is characterized in that in a welding apparatus forbutt welding a first base material and a second base material with eachother, the welding apparatus comprises a welding wire to be introducedinto a groove formed at an area of contact between the first basematerial and the second material, a control device for controlling aposition of the welding wire, a welding power source for feeding weldingelectric power to the area of contact, and control means for outputtinga command to the control device such that the welding wire is movedtoward the second base material when an actual voltage fed from thewelding power source to the area of contact has exceeded a first presetvoltage level set in advance and the welding wire is moved toward thefirst base material when an actual current fed from the welding powersource to the area of contact has exceeded a preset current level set inadvance or the actual voltage has fallen below a second preset voltagelevel set in advance and also for comparing the actual current andvoltage with a preset average current level and preset average voltagelevel set in advance, respectively, and outputting a current controlsignal and voltage control signal to the welding power source such thatthese actual current and voltage become equal to the preset current andvoltage levels set in advance.

A sixteenth aspect is characterized in that in a welding apparatus forbutt welding a first base material and a second base material with eachother, the welding apparatus comprises a welding wire, a welding torchfor holding the welding wire in place, feeding means for feeding thewelding wire to the welding torch, a control unit provided with aposition control device for positionally controlling the welding wire indirections of three orthogonal axes, a welding power source for feedingwelding electric power to an area of contact between the first basematerial and the second base material, an average voltage setting devicefor setting an average voltage level for the welding, an average currentsetting device for setting an average current level for the welding, avoltage detector and current detector for detecting an actual weldingvoltage and actual welding current to form, by the welding wirepositioned facing on a groove formed by a single groove face arranged onthe first base material and a flat surface of the second base material,a bead in a form of a fillet weld on a back side of the groove, a powerdiagnosis unit for being inputted with the actual voltage detected bythe voltage detector and the actual current detected by the currentdetector, outputting a command to the position control device such thatthe welding wire is moved toward the second base material when theactual voltage has exceeded a first preset voltage level set in advanceand the welding wire is moved toward the first base material when theactual current detected by the current detector has exceeded a presetcurrent level set in advance or the actual voltage detected by thevoltage detector has fallen below a second preset voltage level set inadvance, and also outputting the actual voltage and outputting theactual current, the current control device for comparing the averagecurrent level inputted from the average current setting device with theactual current inputted from the power diagnosis unit and outputting acurrent control signal such that this actual current becomes equal tothe preset current level set in advance, a voltage control device forcomparing the average voltage level inputted from the average voltagesetting device with the actual voltage inputted from the power diagnosisunit and outputting a voltage control signal such that this actualvoltage becomes equal to the preset voltage level set in advance, andthe output control device for being inputted with the current controlsignal outputted from the current control device and the voltage controlsignal outputted from the voltage control device, and based on thesecurrent control signal and voltage control signal, outputting a powersource control signal to the welding power source to control an outputof the power source.

According to the fifteenth or sixteenth aspect, while performing arcwelding of the first base material and the second base material from oneside, the center axis of an arc is accurately position-controlled at apredetermined inclination relative to the second base material, and anaverage voltage and average current are also controlled to become equalto their corresponding preset values. It is, therefore, possible tostably form a bead in the form of a fillet weld on the back side of thegroove.

A seventeenth aspect is characterized in that in the sixteenth aspect,the welding apparatus is provided with a peak voltage setting device forsetting a peak voltage for a pulse voltage, a base voltage settingdevice for setting abase voltage, a pulse duration setting device forsetting a pulse duration, and a pulse waveform control device for beinginputted with the preset peak voltage, preset base voltage level andpreset pulse duration from the peak voltage setting device, base voltagesetting device and pulse duration setting device, respectively,comparing these preset values with an actual peak voltage, actual basevoltage and actual pulse duration, respectively, and outputting awaveform control signal to the output control device, the powerdiagnosis unit comprises means for determining an actual peak voltage,actual base voltage and actual pulse duration on a basis of the actualvoltage detected by the voltage detector and the actual current detectedby the current detector, and outputting the thus-determined actual peakvoltage, actual base voltage and actual pulse duration to the pulsewaveform control device, and the output control device comprises meansfor being inputted with the waveform control signal outputted from thepulse waveform control device and outputting a power source controlsignal, which controls an output of the power source, to the weldingpower source on a basis of the voltage control signal inputted from thevoltage control device and the current control signal inputted from thecurrent control device.

An eighteenth aspect is characterized in that in the sixteenth aspect,the pulse waveform control device comprises sinusoidal current formingmeans for converting a welding current into a sinusoidal current,comparing a preset sinusoidal waveform, which has been set in advance,with an actual sinusoidal waveform and outputting a waveform controlsignal to the output control device, the power diagnosis unit comprisesmeans for determining an actual current waveform on a basis of theactual voltage detected by the voltage detector and the actual currentdetected by the current detector, and outputting the thus-determinedactual current waveform to the sinusoidal current forming means, and theoutput control device comprises means for outputting a power sourcecontrol signal, which controls an output of the power source, to thewelding power source on a basis of the waveform control signal inputtedfrom the sinusoidal current forming means, the voltage control signalinputted from the voltage control device and the current control signalinputted from the current control device.

According to the seventeenth or eighteenth aspect, a pulse current isused as an arc welding current so that an arc is provided with higherdirectivity and can more precisely impinge on a position aimed by thearc. Further, the arc can be accurately maintained at a predeterminedinclination. This makes it possible to prevent occurrence of aninconvenience such as a burn-through at the area of contact between thefirst base material and the second base material or remaining ofundeposited parts, and accordingly, to deposit a fillet-weld-shaped beadin a stable form on the back side of the groove.

A nineteenth aspect is characterized in that in a welding apparatus forbutt welding a first base material and a second base material with eachother, the welding apparatus comprises a welding wire to be introducedthrough a welding torch into a groove formed by bringing the first basematerial, on which a root face and a single groove face have beenformed, into contact with the second material having a flat surface, acontrol device for controlling a position of the welding wire, a weldingpower source for feeding welding electric power to the area of contact,a voltage detector for detecting an actual voltage to be fed from thewelding power source to the area of contact, a clock device fordetecting a time, at which an arc from the welding wire passes through aposition of contact between an end portion of the single groove face andthe flat surface, and clocking a time after the arc passes through theposition of contact until the arc moves toward the first base materialand returns back to the predetermined position, memory means for storinga change in welding voltage during the clocking time by the voltagedetector and the clock device, and wire position control means forcontinuing preceding weaving control when a time (t₄−t₃)−t₃ being a timeat which an actual voltage begins to exceed a preset voltage level setin advance and t₄ being a time at which the actual voltage falls belowthe preset voltage level, both while clocking a second predeterminedtime Ät₂ subsequent to an elapse of a first predetermined time Ät₁ froma time point at which the welding wire passed through the position ofcontact during the clocking time—falls within a target time range inwhich adequate fusion takes place without punching through the firstbase material, moving a center axis of weaving of the welding wiretoward the second base material when the time (t₄−t₃) exceeds the targettime, and moving the center axis of weaving toward the first basematerial when the time (t₄−t₃) falls below the target time.

A twentieth aspect is characterized in that in a welding apparatus forbutt welding a first base material and a second base material with eachother, the welding apparatus comprises a welding wire to be introducedthrough a welding torch into a groove formed by bringing the first basematerial, on which a root face and a single groove face have beenformed, into contact with the second material having a flat surface, acontrol device for controlling a position of the welding wire, a weldingpower source for feeding welding electric power to the area of contact,a current detector for detecting an actual current to be fed from thewelding power source to the area of contact, a clock device fordetecting a time, at which an arc from the welding wire passes through aposition of contact between an end portion of the single groove face andthe flat surface, and clocking a time after the arc passes through theposition of contact until the arc moves toward the first base materialand returns back to the predetermined position, memory means for storinga change in welding current during the clocking time by the currentdetector and the clock device, and wire position control means forcontinuing preceding weaving control when a time (t₄−t₃)−t₃ being a timeat which an actual current begins to fall below a preset current levelset in advance and t₄ being a time at which the actual current exceedsthe preset voltage level, both while clocking a second predeterminedtime Ät₂ subsequent to an elapse of a first predetermined time Ät₁ froma time point at which the welding wire passed through the position ofcontact during the clocking time—falls within a target time range inwhich adequate fusion takes place without punching through the firstbase material, moving a center axis of weaving of the welding wiretoward the second base material when the time (t₄−t₃) exceeds the targettime, and moving the center axis of weaving toward the first basematerial when the time (t₄−t₃) falls below the target time.

According to the nineteenth or twentieth aspect, even if a movement ordistortion takes place in the groove in the direction of the width ofthe groove due to restraint conditions for the first base material andthe second base material and/or a thermal distortion or the like duringwelding, the welding can be appropriately corrected to trace a weld linein the groove by moving the welding wire on the basis of the actualvoltage or actual current detected by the actual voltage detector oractual current detector. This makes it possible to more accurately forceout the melt to the back side of the groove and hence, to also form abead in the form of a good fillet weld. As no work is needed for thearrangement of an auxiliary bead, a backing strip or the like and thewelding can be performed by automatically and more accurately tracingthe weld line, the workability of the welding can be improved.

A twenty-first aspect is characterized in that in a welding apparatusfor butt welding a first base material and a second base material witheach other, the welding apparatus comprises a welding wire to beintroduced through a welding torch into a groove formed by bringing thefirst base material, on which a root face and a single groove face havebeen formed, into contact with the second material having a flatsurface, a control device for controlling a position of the weldingwire, a welding power source for feeding welding electric power to thearea of contact, a voltage detector for detecting an actual voltage tobe fed from the welding power source to the area of contact, a clockdevice for detecting a time, at which an arc from the welding wirepasses through a position of contact between an end portion of thesingle groove face and the flat surface, and clocking a time after thearc passes through the position of contact until the arc moves towardthe first base material and returns back to the predetermined position,memory means for storing a change in welding voltage during the clockingtime by the voltage detector and the clock device, and wire tip positioncontrol means for moving a tip of the welding wire away from theposition of contact when an actual average voltage during the clockingtime falls below a preset first voltage level, moving the tip of thewelding wire toward the position of contact when the actual averagevoltage exceeds a preset second voltage level, and maintaining the tipof the welding wire at a preceding position when the actual averagevoltage falls between the preset first voltage level and the presetsecond voltage level.

A twenty-second aspect is characterized in that in a welding apparatusfor butt welding a first base material and a second base material witheach other, the welding apparatus comprises a welding wire to beintroduced through a welding torch into a groove formed by bringing thefirst base material, on which a root face and a single groove face havebeen formed, into contact with the second material having a flatsurface, a control device for controlling a position of the weldingwire, a welding power source for feeding welding electric power to thearea of contact, a current detector for detecting an actual current tobe fed from the welding power source to the area of contact, a clockdevice for detecting a time, at which an arc from the welding wirepasses through a position of contact between an end portion of thesingle groove face and the flat surface, and clocking a time after thearc passes through the position of contact until the arc moves towardthe first base material and returns back to the predetermined position,memory means for storing a change in welding current during the clockingtime by the current detector and the clock device, and wire tip positioncontrol means for moving a tip of the welding wire away from theposition of contact when an actual average current during the clockingtime exceeds a preset first current level, moving the tip of the weldingwire toward the position of contact when the actual average currentfalls below a preset second current level, and maintaining the tip ofthe welding wire at a preceding position when the actual average currentfalls between the preset first current level and the preset secondcurrent level.

According to the twenty-first or twenty-second aspect, even if amovement or distortion takes place in the groove in the direction of thewidth of the groove due to restraint conditions for the first basematerial and the second base material and/or a thermal distortion or thelike during welding, the welding can be appropriately corrected to tracea weld line in the groove by moving the position of the tip of thewelding wire closer or away on the basis of the actual average voltageor actual average current detected by the actual voltage detector oractual current detector. This makes it possible to more accurately forceout the melt to the back side of the groove and hence, to also form abead in the form of a good fillet weld. As no work is needed for thearrangement of an auxiliary bead, a backing strip or the like and thewelding can be performed by automatically and more accurately tracingthe weld line, the workability of the welding can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view illustrating welding work for a “T” joint bya first embodiment of the present invention.

FIG. 2 is a perspective view showing the “T” joint welded by the weldingwork illustrated in FIG. 1.

FIG. 3 is a schematic view showing a state in which the position of awelding wire has been set before initiation of welding in the weldingwork illustrated in FIG. 1.

FIG. 4 is a schematic view depicting a state in which the welding hasbeen initiated in the state shown in FIG. 3.

FIG. 5 is a schematic view showing a state in which the welding hasproceeded further from the state depicted in FIG. 4.

FIG. 6 is a schematic view illustrating an example of butt welding workon plates having different thicknesses in accordance with Example 3 of afirst embodiment of the present invention.

FIG. 7 is a schematic view illustrating another example of the buttwelding work on plates having different thicknesses in accordance withExample 3 of the first embodiment of the present invention.

FIG. 8 is schematic view showing a modification of a weldable grooveshape in the first embodiment of the present invention.

FIG. 9 is schematic view showing another modification of the weldablegroove shape in the first embodiment of the present invention.

FIG. 10 is a schematic view illustrating welding work for a “T” joint bya second embodiment of the present invention.

FIG. 11 is a schematic view illustrating welding work for a “T” joint bya third embodiment of the present invention.

FIG. 12 is a front elevation of a hydraulic excavator equipped withwelded structures fabricated by a welding method according to a fourthembodiment of the present invention.

FIG. 13 is a cross-sectional view taken along XIII—XIII of FIG. 12.

FIG. 14 is a cross-sectional view taken along XIV—XIV of FIG. 12.

FIG. 15 is a cross-sectional view depicting a butt-welded joint betweenupper plates of different thicknesses in a boom of the hydraulicexcavator, said butt-welded joint being designated at sign XV in FIG.12.

FIG. 16 is a diagram showing the construction of a welding apparatusaccording to a fifth embodiment of the present invention.

FIG. 17 is a schematic view illustrating an example of weaving operationof a welding wire in the welding apparatus shown in FIG. 16.

FIG. 18 is a diagram showing a relationship between the weaving positionof the welding wire and the welding voltage generated in the weldingwire under such welding conditions that minimize the forcing-out of amelt to the back side of a groove by the welding apparatus shown in FIG.16.

FIG. 19 is a diagram showing a relationship between the weaving positionof the welding wire and the welding voltage generated in the weldingwire under such welding conditions that maximize the forcing-out of amelt to the back side of a groove by the welding apparatus shown in FIG.16.

FIG. 20 is a flow chart illustrating a control procedure for the weavingposition of the welding wire in the welding apparatus shown in FIG. 16.

FIG. 21 is a flow chart illustrating a continuation of the controlprocedure of FIG. 20.

FIG. 22 is a diagram showing the construction of a welding apparatusaccording to a sixth embodiment of the present invention.

FIG. 23 is a waveform diagram of a pulse current in the weldingapparatus shown in FIG. 22.

FIG. 24 is a diagram illustrating, as a graph, a relationship betweenthe leg length of a bead in the form of a fillet weld as formed on theback side of a groove and the aimed point of a welding apparatus towhich a welding method according to the present invention is applied.

BEST MODES FOR CARRYING OUT THE INVENTION

A description will hereinafter be made about embodiments of the presentinvention.

1. First Embodiment

FIG. 1 through FIG. 9 are drawings for illustrating a welding methodaccording to a first embodiment of the present invention.

FIG. 1 is a schematic view illustrating welding work for a “T” joint bythe first embodiment of the welding method of the present invention, andFIG. 2 is a perspective view showing the “T” joint welded by the weldingwork illustrated in FIG. 1.

FIG. 1 illustrates a state upon welding a first base material 1 and asecond base material 2 with each other by bringing them into abutment inthe form of “T”. The first base material 1 is provided at a butted endportion thereof with a root face 1 a and a single groove face 1 b whichserves to form a single bevel groove. The second base material 2 has aflat surface 2 a positioned in contact with the root face 1 a of thefirst base material 1, and in combination with the first base material1, forms a “T” joint. Numeral 5 designates a welding torch, and numeral6 indicates a welding wire held in place by the welding torch 5 and fedby unillustrated feeding means. In FIG. 1, there are also indicated adimension Rf in the direction of the thickness of the root face 1 a, aposition P₁ of contact between an end portion of the single groove face1 b of the first base material 1 and the flat surface 2 a of the secondbase material 2, a point P₂ aimed by the center axis of an arc, and adistance d from the contact position P₁ to the aimed point P₂ by thecenter axis of the arc. Also shown are a groove angle è, a predeterminedinclination ä between the center axis of the arc (welding wire) and theflat surface 2 a of the second base material 2, and the center axis A ofthe arc.

With reference to the drawings, a description will hereinafter be madebased on specific examples.

1.2 First Example

In this example, the first and second base materials 1, 2 were made ofsteel, and the dimension Rf of the root face 1 a was 1 mm. By settingthe root gap at 0 mm (in other words, the root face was in a contactedposition) and the groove angle è at 45 degrees, CO₂ arc welding wasconducted with the welding apparatus. As welding conditions, the averagewelding current was set at 310 A, the average welding voltage at 33 V,and the moving speed at 35 to 40 cm/min.

Under the above conditions, it was possible to stably deposit a bead inthe form of a fillet weld of 2 to 8 mm at an area of abutment between aside 1 c of the first base material 1, said side being located on a sideopposite to the groove, and the flat surface 2 a of the second basematerial 2 when the aimed point P₂ by the welding wire 6 (the centeraxis of the arc) was set 0 to 3 mm apart from the contact position P₁,the second base material 2 was placed in a substantially horizontalposition, and the predetermined inclination ä formed between the flatsurface 2 a and the welding wire 6 was set at 15 to 35 degrees.

The results of the welding are shown in FIG. 2. FIG. 2 illustrates abead B4 deposited in the form of a fillet weld between the side 1 c ofthe base material 1, said side being located on a side opposite to thegroove, and the flat surface 2 a of the second base material 2, a beadB5 resolidified while causing the flat surface 2 a of the second basematerial 2 to fuse, and a bead B6 formed on the side of the groove withaddition of a melt from fusion of the welding wire 6 itself subsequentto the formation of the bead B4.

It is to be noted that the above-described specific values should bedetermined by taking into consideration various conditions such as theplate thicknesses of the first and second base materials 1,2 and theshape of the area of abutment between the first base material 1 and thesecond base material 2.

The process of formation of the beads on the “T” joint in this exampleis shown in FIG. 3 to FIG. 5.

FIG. 3 is a schematic view showing a state in which the position of thewelding wire has been set before initiation of welding in the weldingwork illustrated in FIG. 1. As illustrated in FIG. 3, the welding wire 6is positioned opposite the groove by setting the aimed point P₂ of thewelding wire 6 at a point a little apart toward the welding directionfrom the position P₁ of contact between the end portion of the grooveface 1 b and the flat surface 2 a and tilting the direction of thewelding wire at the predetermined inclination ä relative to the flatsurface 2 a of the second base material 2 the thermal capacity of whichis greater.

FIG. 4 is a schematic view depicting a state in which welding has beeninitiated in the above-mentioned state shown in FIG. 3. Because thewelding wire 6 is directed toward the flat surface 2 a as depicted inFIG. 4, more heat is inputted in the flat surface 2 a than in the singlegroove face 1 b the thermal capacity of which is smaller. While bothbase materials 1,2 are being caused to fuse in a well-balanced manner, amolten pool is hence formed with addition of a melt from fusion of thewelding wire 6 itself. As a result, on the side of the first basematerial 1 having the single groove face 1 b of smaller thermalcapacity, a fusion zone reaches the back side 1 c which is located onthe back side of the groove.

FIG. 5 is a schematic view showing a state in which the welding hasproceeded further from the state depicted in FIG. 4. As shown in FIG. 5,the molten pool is forced out to the side opposite to the welding side,i.e., to the back side of the first base material 1 by the force of thearc, convection in the molten pool, and the like, and under the actionof surface tension and the like, a molten pool is formed extendingintegrally from the inside of the groove to the back side of the basematerial 1. The melt then resolifies so that beads B4, B5 and B6 such asthose shown in FIG. 2, namely, a first layer of the “T” joint is formed.

The above-described welded state corresponds to the welding of a firstlayer in the groove. Depending on the size of the groove, the welding ofthe remaining portion in the groove can be conducted in a similar manneras in the conventional art, and therefore, its description is omitted.

1.2 Second Example

As a second example, the following example can be given.

Under conditions that CO₂ arc welding was chosen as a welding process,the root face Rf was set at 1 mm, the root gap was set at 0 mm, thegroove angle è was set at 45 degrees, the average current was set at 310A, the average voltage was set at 33 V, the welding speed was set at 35cm/min, the aimed point P₂ of the welding wire 6 was set at a point 2 mmapart from the contact position P₁ (d=2 mm), and the inclination a wasset at 25 degrees, a “T” joint was welded from the side of the groove.When welded as described above, a bead B4 in the form of a fillet weld,which had a leg length of 7 mm in the vertical direction (on the side ofthe first base material 1) and a leg length of 5 mm in the horizontaldirection (on the side of the second base material 2), was successfullydeposited between the back side 1 c of the first base material 1, saidback side being located on the back side of the groove, and the flatsurface 2 a of the second base material 2 without leaving anyundeposited part in the groove. It was also possible to obtain a bead B4in the form of a fillet weld in a relatively stable manner by settingthe aimed point P₂ of the welding wire 6 at a position 2 to 3 mm apartfrom the contact position P₁.

1.3 Third Example

A third example is shown in FIG. 6 and FIG. 7.

FIG. 6 and FIG. 7 are drawings, each of which illustrates the thirdexample in which two plates having different thicknesses arebutt-welded. In FIG. 6, a first base material 1′ consisting of a plateand a second base material 2′ having a greater thickness than the firstbase material 1′ are kept in abutment against each other with one sidesthereof being arranged on the same plane. The drawing also shows a rootface 1′a of the base material 1′, a groove 1′b arranged on one side ofan abutted portion of the base material 1′, a side 1′c of the basematerial 1′, said side being located on a side opposite to the groove1′b, and a flat surface 2′a of the second base material 2′. In thebutt-welded joint shown in FIG. 6, a bead B4′ can also be deposited atan area, where the joint is desired, to form the joint even by one-sidewelding from the side of the groove if the aimed point of the weldingtorch 5, i.e., the welding wire 6, the relationship of the welding torch5, i.e., the welding wire 6 with the groove, and the like are set asconditions as illustrated in FIG. 1 which has been described above.

In the example of FIG. 7 in which the two plates are butt-welded, bothof the base materials 1′, 2′ are arranged with one sides thereofextending in parallel with each other, and the thinner one of both ofthe base materials 1′, 2′, that is, the first base material 1′ ispositioned adjacent a center of the thicker, second base material 2′ asviewed in the direction of its thickness such that they are kept inabutment against each other.

FIG. 7 is similar to the above-mentioned example illustrated in FIG. 6,but is different only in the final bead shape on the side of the groovein the welded joint. Accordingly, a description of the example of FIG. 7is omitted. In the example of FIG. 7, the welding only from the side ofthe groove, in other words, from the one side can also form the weldedjoint as a joint which permits well-balanced transmission of force owingto the registration between the centers of the plates as viewed in thedirections of their thicknesses.

1.4 Fourth Example

Other examples of the groove shape weldable by the welding method of thepresent invention will next be shown in FIG. 8 and FIG. 9.

FIG. 8 shows an example in which a J-shaped, single groove face 1 b 1 isarranged on a first base material 1, while FIG. 9 illustrates an examplein which a single groove face 1 b 2 is arranged with plural straightlines. In each of these examples, a desired root face 1 a is arranged.Similarly to the above-mentioned case of the single bevel groove, a beadB4 in the form of a fillet weld can, therefore, be formed by arc weldingfrom one side between a back side 1 c of the first base material 1, saidback side being located on the back side of the groove, and a flatsurface 2 a of a second base material 2 even if the groove shape isother than a single bevel groove.

1.5 Aimed Point P₂ and the Results of Welding

FIG. 24 is a diagram illustrating, as a graph, a relationship betweenthe leg length of a bead in the form of a fillet weld as formed on theback side of a groove and the aimed point of a welding apparatus towhich a welding method according to the present invention is applied.

As shown in FIG. 24, the leg length of the bead B4 to be formed betweenthe back side 1 c of the first base material 1, said back side beinglocated on the back side of the groove, and the flat surface 2 a of thesecond base material 2 is formed in a range of from about 4 to 7 mm inthe vertical direction when the distance d between the contact positionP₁ and the aimed point P₂ is in a range of from 2 to 5 mm. Even when thedistance d between P₁ and P₂ exceeds 4 mm, the bead B4 can still beformed between the back side 1 c of the first base material 1 and theflat surface 2 a of the second base material 2 although the leg lengthof the bead B4 is undesirably shortened to 1 mm or so in the horizontaldirection. Further, this bead B4 is formed with a desired horizontal leglength of about 4 mm or so when the distance d between P₁ and P₂ is in arange of from 2 to 3 mm.

As described above, owing to the difference in thermal capacity betweenthe first base material with the single groove face 1 b arranged thereonand the second base material having the flat surface 2 a and the fusionof the welding wire, this embodiment makes it possible to weld thegroove and also to stably deposit the bead B4 in the form of a filletweld between the back side 1 c of the first base material 1, said backside being located on the back side of the groove, and the flat surface2 a of the second base material 2.

Described specifically, a greater portion of an arc is caused togenerate on (a greater portion of the heat of an arc is caused to betransferred to) the side of the second base material 2 of larger thermalcapacity. On the side of the single groove face 1 b of the first basematerial 1 of smaller thermal capacity, the base material 1 is caused tofuse wholly to the back side 1 c on the back side of the groove to suchan extent that no punch-through takes place, and further, fusion of thewelding wire 6 forces a melt out to the back side of the groove whilefilling up the groove. The bead B4 in the form of the fillet weld can beformed accordingly.

If there is a further part to be welded in another groove, its weldingin a similar manner as in conventional art makes it possible to form adesired “T” joint.

On the inner side of a box-shaped, welded structure, beads in the formof fillet welds can, therefore, be deposited in a groove and on the backside of the groove, respectively, by simply arranging the groove on theouter side of a joint to be butt-welded and conducting arc welding fromthe side of the groove. As a consequence, a joint can be fabricatedwhile retaining the strength, and no work is needed to arrange a bead inadvance and hence, the efficiency of the welding work can besignificantly improved.

Even in such a structure that includes such a joint part as permittingno welding from the back side of a groove and thus unavoidably requiringuse of thicker base materials for being to be welded together, a bead inthe form of a fillet weld can also be deposited on the back side of thegroove by performing arc welding only from one side without leaving anypart undeposited in the groove. It is, therefore, possible to reduce thethicknesses of base materials without a reduction in the strength of theresulting structure.

2. Second Embodiment

FIG. 10 is a schematic view illustrating a second embodiment of thewelding method according to the present invention, and shows weldingwork for a “T” joint. In this embodiment, elements equivalent to thecorresponding elements in the above-described first embodiment aredesignated by like reference signs, and overlapping descriptions areomitted.

In this second embodiment, a welding wire 6 held in place on a weldingtorch 5 and fed by unillustrated feeding means is held at an inclinationa relative to a flat surface 2 a of a second base material 2 while beingdirected to an aimed point P₂. In this embodiment, welding is performedwhile causing the welding wire 6 to weave. The weaving is effected bydriving the welding torch 5 under control such that the welding wire 6oscillates at a predetermined amplitude in the direction of an arrow 50while maintaining the above-described inclination ä. The amplitude andpitch of oscillation for the weaving are determined depending on thethickness of a first base material 1, the size of a groove, etc.

Even when welding is performed while causing the welding wire 6 to weaveas described above, an arc is directed more toward the side of the flatsurface 2 a of the second base material 2 of greater thermal capacitywhile the predetermined inclination ä is always maintained. As theoscillation is effected in this state, a molten pool is forced out tothe back side of the groove so that a bead B4 in the form of a filletweld can be deposited between the back side 1 c of the first basematerial 1, said back side being located on the back side of the groove,and the flat surface 2 a. In this manner, efficient welding is feasibleeven where the groove angle è is rather large.

As an alternative, the welding wire 6 can also be caused to weave in thedirection of its axis as indicated by an arrow 60 in the same drawing,that is, FIG. 10. In this case, a bead B4 in the form of a fillet weldcan also be caused to deposit between the back side 1 c of the firstbase material 1, said back side being located on the back side of thegroove, and the flat surface 2 a of the second base material 2 byforcing out a molten pool to the back side of the groove under arc forceor the like.

3. Third Embodiment

FIG. 11 is a schematic view illustrating a third embodiment of thewelding method according to the present invention, and shows weldingwork for a “T” joint. In this embodiment, elements equivalent to thecorresponding elements in the first and second embodiments aredesignated by like reference signs, and overlapping descriptions areomitted.

In the third embodiment, weaving of a welding wire 6 is performed bydriving a welding torch 5 under control such that a tip of a weldingwire 6 is swung in the form of a circular arc over á degrees about apredetermined inclination ä as a center. In this third embodiment, abead B4 in the form of a fillet weld can also be deposited between aback side 1 c of a first base material 1, said back side being locatedon the back side of the groove, and a flat surface 2 a as in theabove-mentioned embodiments.

4. Fourth Embodiment

FIG. 12 is a front elevation of a hydraulic excavator as a weldedstructure fabricated by the welding method according to the presentinvention.

In FIG. 12, the hydraulic excavator comprises a travel base 70, anupperstructure 71 mounted for revolution on the travel base 70, and arevolving mechanism 72 for causing the upperstructure 71 to revolve.This revolving mechanism 72 can cause the upperstructure 71 to revolveover 360 degrees relative to the travel base 70. The travel base 70 isprovided with a travel track frame, drive wheels arranged on the traveltrack frame, crawlers wrapped on the drive wheels, etc., and allows thehydraulic excavator to travel.

The upperstructure 71 has an unillustrated revolving frame, and isprovided with various hydraulic equipment such as an engine andhydraulic pumps, an operator's cab 73, etc. By operating control devicesarranged in the operator's cab 73, an operator can drive the travel base70, working equipment 80 to be described subsequently herein, and thelike. The working equipment 80 is generally constructed of a boom 74arranged pivotally up and down on the upperstructure 71, a boom cylinder75 for driving the boom 74, an arm 76 pivotally arranged on the boom 74,an arm cylinder 77 for driving the arm 76, a bucket 78 attached to thearm 76, a bucket cylinder 79 for driving the bucket 78, and the like.

Elements making up the above-described hydraulic excavator, such as thetrack frame, the revolving frame, the boom 74 and the arm 76, are weldedstructures formed by combining welded joints typified by “T” joints. Astheir cross-sectional shapes are approximately box-shaped in manyinstances, it is difficult to arrange auxiliary beads, backing strips orthe like on their back sides. The present invention can, however,overcome this difficulty.

FIG. 13 is a cross-sectional view taken along XIII—XIII of FIG. 12, FIG.14 is a cross-sectional view taken along XIV—XIV of FIG. 12, and FIG. 15is a cross-sectional view of a part designated at sign XV in FIG. 12.More specifically, FIG. 13 is across-sectional view of the boom 74 ofthe hydraulic excavator in FIG. 12, FIG. 14 is a cross-sectional view ofthe arm 76 of the hydraulic excavator in FIG. 12, and is across-sectional view showing a butt-welded joint part of upper platesthemselves of different thicknesses in the boom of the hydraulicexcavator. These boom 74 and arm 76 are in the forms of box-shaped,welded structures, and in FIG. 15, a butt-welded joint between a thickplate member 74 a′ and a thin plate member 74 a″, both of which make upan upper plate of the boom 74, is formed.

The boom 74 is constructed of an upper plate 74 a, a left and right sideplates 74 b, 74 b, and a lower plate 74 c. Upon forming the boom 74 byapplying the welding method of the present invention, each side plate 74b with a root face formed thereon and also with a single groove facearranged on an outer side thereof is brought into abutment against thelower plate 74 c having a flat surface, and welding work is performedfrom the side of the groove by using the above-mentioned welding methodshown in FIG. 1. This welding work can form a bead 74 g in the groovebetween the single groove face of the side plate 74 b and the flatsurface of the lower plate 74 c, and can also deposit a bead B74 in theform of a fillet weld between the inner wall of the side plate 74 b andthe flat surface of the lower plate 74 c. According to this embodiment,a box-shaped, welded structure welded also on the inner side of thestructure can be fabricated by welding work only from the outside of thestructure without needing arranging a backing strip or arranging a beadfor the prevention of a burn-through, a punch-through or the like andfurther, without needing arranging an access hole or the like for aworker to perform welding on the side plates 47 b inside the structure.

Needless to say, the present invention can also be applied to thewelding between the upper plate 74 a and the side plates 74 b. When awelding torch or the like can be inserted between both of the sideplates 74 b, 74 b and a sufficient space is available there, it ispossible, as in the conventional art, to bring the side plates 74 b, 74b, on outer sides of which grooves are arranged, into abutment againstthe upper plate 74 a to perform fillet welding to the grooves from theoutside and then to perform fillet welding from the back sides of thegrooves.

On the other hand, the arm 76 is constructed of a square U-shaped member76 a, which forms a box-shaped structure and has been formed by pressingor the like, and a plate-shaped member 76 c which makes up the remainingone side. Upon forming the arm 76 by the welding method of the presentinvention, the member 76 a with root faces formed thereon and also withsingle groove faces formed on the outer sides of the root faces isbrought into abutment against the lower plate 76 c having a flatsurface, and by using the above-mentioned welding method shown in FIG.1, welding is performed from the side of the grooves. By this welding,beads 76 g can be formed in grooves between the single groove faces ofthe member 76 a and the flat surface of the lower plate 76 c, andfurther, beads B76 in the form of fillet welds can also be depositedbetween the surfaces on the back side of the grooves of the member 76 aand the flat surface of the lower plate 76 c.

As has been described above, even in a welded structure such as thatillustrated in FIG. 14, a box-shaped, welded structure welded also onthe inner side of the structure can be fabricated by welding work onlyfrom the outside of the structure without needing arranging backingstrips or arranging beads for the prevention of a burn-through, apunch-through or the like and further, without needing arranging anaccess hole or the like for a worker to perform welding on the sideportions of the member 76 a inside the structure.

FIG. 15 is a cross-sectional view depicting the butt-welded joint of theupper plates themselves of different thicknesses in the boom of thehydraulic excavator, said butt-welded joint being designated at sign XVin FIG. 12. It is the butt-welded joint of the thick plate member 74 a′and the thin plate member 74 a″, both of which make up the upper plateof the boom 74. Both of the members 74 a′, 74 a″ are kept in abutment atend portions thereof such that as viewed in the drawing, their lowersurfaces lie in the same plane. The member 74 a″ is provided with asingle groove face 74 k. In this embodiment, the thick plate member 74a′ is provided with a tilted surface extending toward an area of itsabutment with the thin plate member 74 a″, for example, between aposition T1 and a position T2 so that no extreme change occurs instrength.

In the welded joint illustrated in FIG. 15, the welding methodillustrated with reference to FIG. 6 in connection with the thirdexample of the first embodiment is applied, and welding is performedfrom the side of the groove 74 k such that an arc is generated at apredetermined inclination relative to the butted end face of the member74 a′. As a result, a bead B74′ in the form of a fillet weld can beformed between the butted end face of the member 74 a′ and the back sideof the member 74 a″, said back side being located on a side opposite thesingle groove face 74 k.

5. Fifth Embodiment

FIG. 16 through FIG. 21 are intended to describe a fifth embodiment ofthe present invention. In this embodiment, elements equivalent to thecorresponding elements described above are designated by like referencesigns, and overlapping descriptions are omitted.

5.1 Overall Construction

FIG. 16 is a diagram showing the outline construction of a weldingapparatus according to this embodiment. In the drawing, the weldingapparatus is constructed basically of a robot main body 3, a robotcontroller 4, and a first and second base materials 1, 2 to be welded.The first base material 1 is provided at an end portion on its abuttedside with a single groove face 1 b which serves to form a single bevelgroove. A portion of the second base material 2, said portion being keptin abutment with the first base material 1, is formed as a flat surface.

The robot main body 3 is constructed such that it can perform revolutionand pitching. The robot main body 3 is provided with a parallel linkmechanism 3A, and on the parallel link mechanism 3A, a robot arm 3B isarranged. Further, the robot main body 3 is controlled by the robotcontroller 4. This robot controller 4 is arranged to output commandsignals such that the robot arm 3B is driven under control in thedirections of at least three orthogonal axes X, Y, Z shown in thedrawing. The robot controller 4 is provided with an input unit 4A forinputting and storing various preset values and the like for control, aposition control unit 4B for controlling the position and attitude ofthe robot arm 3B, a speed control unit 4C for controlling the weldingspeed, etc. A welding torch 5 is arranged on a free end of the robot arm3B, a welding wire 6 is held in place on the welding torch 5, and thewelding wire 6 is fed by a feeder 8 through the torch 5. Designated atsigns 7A and 7B are cables for feeding welding electric power. The cable7A is connected to the welding wire 6 on the side of the feeder 8 whichthe robot is provided with, while the cable 7B is connected to the basematerial 1 or 2 to be welded. The cables 7A, 7B are connected to awelding power source 9, thereby connecting the welding wire 6 and thebase material 1 or 2 to the welding power source 9. A voltage detector10 and current detector 11 are attached to the cable 7A, so that thevoltage of a welding current to be fed from the welding power source 9to the welding wire 6 is detected by the voltage detector 10 and thewelding current to be fed from the welding power source 9 to the weldingwire 6 is detected by the current detector 11. Incidentally, the weldingvoltage and welding current so detected are inputted to a powerdiagnosis unit 23.

At a preceding stage of the welding power source 9, an output controldevice 22 is arranged. At a preceding stage of the output control device22, a voltage control device 13 and current control device 15 arearranged in parallel with each other. At a preceding stage of thevoltage control device 13, an average voltage setting device 12 isarranged, and at a preceding stage of the current control device 15, anaverage current setting device 14 is arranged. The average voltagesetting device 12 sets an average level of an voltage to be fed to thewelding wire 6. The voltage control device 13 compares the averagevoltage level set at the average voltage setting device 12 with anactual average voltage inputted via the below-described power diagnosisunit 23 on the basis of an actual voltage detected by the voltagedetector 10, and outputs a voltage control signal. The average currentsetting device 14 sets an average level of a current to be fed to thewelding wire 6, and the current control device 15 compares the averagecurrent level set at the average current setting device 14 with anactual average current inputted via the below-described power diagnosisunit 23 on the basis of an actual current detected by the currentdetector 11, and outputs a current control signal. Inputted to theoutput control device 22 are the voltage control signal from the voltagecontrol device 13 and the current control signal from the currentcontrol device 15. Based on these control signals, the output controldevice outputs a control signal to control electric power to be fed fromthe welding power source 9.

The power diagnosis unit 23, to which detection outputs are inputtedfrom the voltage detector 10 and current detector 11, is composed of aninput unit 23A, a comparison unit 23B and an output unit 23C. The inputunit 23A sets a first preset voltage level higher in voltage than theaverage voltage level set by the average voltage setting device 12, asecond preset voltage level lower in voltage than the average voltagelevel set by the average voltage setting device 12, and a preset currentlevel higher in current than the average current level set by theaverage current setting device 14. The comparison unit 23B compares anactual voltage inputted from the voltage detector 10 with theabove-described, first and second preset voltage levels, and outputs aposition control signal, which is to be described subsequently herein,to the robot controller 4. Further, the comparison unit compares anactual current inputted from the current detector 11 with theabove-described, first preset current level or second preset voltagelevel, and outputs a position control signal to the robot controller 4.The output unit 23C outputs the detected actual voltage and actualcurrent from the voltage detector 10 and current detector 11 to thevoltage control unit 13 and current control unit 15, respectively. Inaddition, the welding apparatus is equipped with a computer or the like,which systematically controls the individual controller and controldevices, the robot and the like.

5.2 Operation

Welding operation which makes use of the welding apparatus constructedas described above is performed as will be described hereinafter.

In FIG. 16, the welding torch 5 is mounted on the robot arm 3B. Thewelding wire 6 is held in place on the welding torch 5, extends over apredetermined length from the free end of the welding torch 5, and isfed by the welding wire feeder 8. As illustrated in FIG. 1, the weldingwire 6 is inserted into a groove formed as a result of contact between afirst base material 1, on which a single groove face 1 b is formed, anda second base material 2 having a flat surface 2 a. At this time, thewelding wire 6 is arranged such that it is tilted at a predeterminedinclination ä relative to the flat surface 2 and is directed toward apredetermined, aimed point P₂. Such a position control is performed bythe input unit 4A and position control unit 4B in the robot controller4. Further, a moving path and welding speed are inputted from the inputunit 4A to the speed control unit 4C, and based on them, the weldingwire 6 is caused to move in a direction perpendicular to the drawingsheet. From the input unit 23A in the power diagnosis unit 23, first andsecond, preset voltage levels and current levels are inputted inadvance, and they are stored in the comparison unit 23B.

With the welding apparatus preset as described above, arc welding of afirst layer is initiated. As soon as the welding begins, the voltagedetector 10 and current detector 11 detect an actual voltage and actualcurrent in the cable 7A, respectively. If the welding wire 6 is causedto move too much, for example, toward the side of the groove of thefirst base material 1 during the welding due to vibrations of the robotor positional displacements of the first and second base materials 1,2,an end portion of the first base material 1 of smaller thermal capacity,said end portion being located on the side of the single groove face 1b, is caused to burn through, thereby making it impossible to form abead. When the end portion of the first base material 1, said endportion being located on the side of the single groove face 1 b,undergoes a burn-through, the arc strikes through the first basematerial 1 to its back side so that the actual voltage becomes higher.The comparison unit 23B in the power diagnosis unit 23 compares thefirst and second preset voltage levels, which were inputted in advance,with the actual voltage and, if the actual voltage exceeds the firstpreset voltage level, outputs a position control signal to the positioncontrol unit 4B in the robot 3 such that the welding wire 6 is caused tomove toward the second base material 2. As a result, the welding wire 6is corrected in position such that it moves from the side of the firstbase material 1 toward the second base material 2.

If the relative positional relationship between the welding wire 6 andthe first and second base materials 1,2 is changed such that the weldingwire 6 is conversely caused to move from the preset position toward theside of the second base material 2, a thermal input into the first basematerial 1 is reduced so that a melt is no longer forced out to the backside of the groove and the melt accumulates on the near side. This leadsto a decrease in the extension of the welding wire 6, resulting inoccurrence of a phenomenon that the actual voltage becomes lower and theactual current becomes higher. The comparison unit 23B then compares thepreset voltage levels, which were inputted beforehand, with the actualvoltage and, if the actual voltage falls below the second preset voltagelevel, outputs a position control signal to the position control unit 4Bsuch that the welding wire 6 is caused to move toward the groove. As aresult, the welding wire 6 is corrected in position to move toward thefirst base material 1. As an alternative, because the actual current hasbeen detected by the current detector 11, the comparison unit 23Bcompares the preset current level, which was inputted in advance, withthe actual current and, if the actual current is higher than the presetcurrent level, outputs a position control signal to the position controlunit 4B such that the welding wire 6 is caused to move toward the firstbase material 1. The welding wire 6 may be corrected in position to movetoward the first base material 1 in this manner.

The output unit 23C in the power diagnosis unit 23, on the other hand,outputs the actual voltage and actual current, which have been detectedby the voltage detector 10 and current detector 11, to the voltagecontrol device 13 and current control device 15, respectively. At thevoltage control device 13, the preset average voltage level and theactual voltage are compared with each other to output a voltage controlcommand signal to the output control device 22 such that the actualvoltage becomes equal to the preset average voltage level. The currentcontrol device 15, on the other hand, compares the preset averagecurrent level and the actual current with each other, and outputs acurrent control command signal to the output control device 22 such thatthe actual current becomes equal to the preset average current level.Based on the voltage control command signal and current control commandsignal so inputted, the output control device 22 outputs control signalsto the welding power source 9 to adjust the voltage and current to befed from the welding power source 9 so that the electric power to be fedis adjusted to the preset values.

In the welding apparatus according to this embodiment, welding isperformed while correcting the positional relationship between thewelding wire 6 and the first and second base materials 1,2 by moving thewelding wire to the preset position and also while correcting theaverage voltage and average current to the present values, as describedabove. By conducting welding only from the side of the groove, stablewelding can therefore be performed without leaving any undeposited partin the groove while depositing a bead in the form of a fillet weld onthe back side 1 c of the first base material 1, which is located on theback side of the groove, and the flat surface 2 a of the second basematerial 2.

5.3 Welding Under Weaving

With the welding apparatus according to this embodiment, welding canalso be performed while causing the welding wire 6 to weave. Weaving iseffected as explained above with reference to FIG. 10, namely, bycausing the welding torch 5 and welding wire 6 to oscillate with apredetermined oscillation width as indicated by the arrow 50 or arrow 60while keeping their attitudes tilted at a predetermined inclination ä oras explained above with reference to FIG. 11, namely, by causing thewelding wire 6 to oscillate and swing tracing a circular arc about theinclination ä as a center. These weaving operations are effected bycontrol signals transmitted from the position control unit 4B to therobot on the basis of the input signals inputted beforehand from theinput unit 4A of the robot 3.

Examples of the weaving are shown in FIG. 17 and FIG. 18. FIG. 17 is aschematic view illustrating an example of weaving operation of a weldingwire by the welding apparatus shown in FIG. 16, and FIG. 18 is a diagramshowing a relationship between the weaving position of the welding wireand the welding voltage generated in the welding wire under weldingconditions which minimize the forcing-out of a melt to the back side ofa groove by the welding apparatus shown in FIG. 16.

The characteristics indicated by a solid line in FIG. 18 indicate therelationship between the weaving position (time) and the welding voltagegenerated in the welding wire 6 in the case that, as illustrated in FIG.17, a center of oscillation width of weaving when the welding torch 5and welding wire 6 were tilted at the predetermined inclination ärelative to the flat surface 2 a of the second base material 2 and weredirected toward the aimed point P₂ was designated by L₀ and the weldingtorch 5 and welding wire 6 were caused to oscillate from the center L₀to the position L₁ on the side of the first base material 1 and in thecase that the welding torch 5 and welding wire 6 were caused tooscillate from the center L₀ to a position L₂ on the side of the secondbase material 2. To simplify the description, the diagram represents acase in which the predetermined inclination a was set at ½ of the angleof the single bevel groove on the first base material 1 and the weavingcenter L₀ shown in FIG. 17 was set at a position directed toward theaimed point P₂.

The characteristics indicated by a dashed curve in FIG. 18, on the otherhand, indicate the relationship between the weaving position (time) andthe welding voltage generated in the welding wire 6 in the case that theinclination ä of the welding wire 6 was set at ½ of the angle of thesingle bevel groove as in the above-mentioned cases, the aimed point ofthe welding wire 6 was set at the position of contact P₁ where the endportion of the single groove face 1 b is in contact with the flatsurface 2 a of the second base material 2, the weaving center of thewelding wire 6 was set at L_(0′) (not shown; this will apply equallyhereinafter), and the welding wire 6 was caused to oscillate from thecenter L_(0′) to a position L_(1′) on the side of the first basematerial 1 and in the case that the welding wire 6 was caused tooscillate to a position L_(2′) of the second base material 2(L_(1′)=L_(2′)). In those cases, however, the welding conditions wereselected such that the forcing-out of a melt to the back side of thegroove by an arc would be minimized.

Now assume that weaving is performed with the aimed point set at thecontact position P₁. When the weaving center L_(0′) is directed towardthe contact position P₁, the welding wire 6 located at the center L_(0′)defines a relatively longest distance from the tip of the welding wire 6to the groove and therefore, the welding voltage takes the highest valueas indicated by the dashed line in FIG. 18. If the welding wire 6 iscaused to oscillate toward the first base material 1 subsequently, thedistance between the tip of the welding wire 6 and the first basematerial 1 becomes gradually shorter so that, as indicated by the dashedline in FIG. 18, the voltage gradually drops and becomes lowest at theposition L_(1′) where the welding wire 6 is located closest to the firstbase material 1. When the welding wire then begins to return toward thesecond base material 2, the voltage, as indicated by the dashed line inFIG. 18, gradually rises back and becomes highest again at the centerL_(0′) of oscillation, and then becomes lowest at the position L_(2′)where the welding wire is located closest to the second base material 2.This is repeated.

A description will next be made of a weaving operation when, asillustrated in FIG. 17, the aimed point of the welding wire 6 was set atP₂, the position where the inclination angle was ä was set at theweaving center L₀ and the welding wire 6 was caused to oscillate fromthe center L₀ to the position L₁ on the side of the first base material1, and also of a weaving operation when the welding wire 6 was caused tooscillate to the position L₂ on the side of the second base material 2.

When the welding wire 6 is located at the weaving center L₀, thedistance between the tip of the welding wire 6 and the groove is not themaximum. As shown in FIG. 18, the voltage in the above case, therefore,takes a value which corresponds to the distance. As the welding wirethen moves toward the first base material 1, the voltage, as indicatedby the solid curve in FIG. 18, gradually rises, and reaches the maximumvoltage when the welding wire 6 has directed toward the contact positionP₁. The voltage then gradually drops up to the position L₁, and when thewelding wire then begins to return toward the second base material 2,the voltage reaches the maximum voltage again at the contact positionP₁. Because the welding wire thereafter gradually moves closer to thesecond base material 2, the voltage drops to the lowest voltage at theposition L₂. This is repeated.

The relationship between the position of the welding wire 6 and thevoltage can be determined either empirically or by calculation inaccordance with preset conditions such as the groove shape, the aimedpoint and the inclination. These values are set beforehand from theinput unit 23A to the comparison unit 23B in the power diagnosis unit23.

Here, it is to be noted that positional control on the welding torch 5for the above-described weaving is set beforehand from the input unit 4Ato the position control unit 4B in the robot controller 4. Further,welding voltages are detected by the voltage detector 10, and based onthe detection values, actual voltages and an actual average voltage aredetermined by the comparison unit 23B. By a comparison between an actualvoltage and a preset average voltage level, the comparison unit 23Bdetermines whether or not an actual aimed point is correct. When anoffset has occurred, a position control signal is outputted to theposition control unit 4B of the robot controller 4, and the weldingtorch is controlled such that the aimed point is brought intoregistration with the preset position.

Further, an actual average voltage V₀ is determined by the comparisonunit 23B of the power diagnosis unit 23 on the basis of detection valuesof the voltage detector 10. The value V₀ is outputted to the voltagecontrol device 13 via the output unit 23C, and from the voltage controldevice 13, a command signal is outputted to the output control device 22such that the actual voltage becomes equal to the preset average voltagelevel as described above. The voltage is adjusted accordingly.

In the above-described case, the welding conditions were selected suchthat the forcing-out of a melt to the back side of a groove by an arcwould become minimum. When the welding conditions are selected such thata bead will be formed to the maximum on the back side of a groove, onthe other hand, and further, when the weaving center L₀ shown in FIG. 17is located on the contact position P₁ (in other words, the weavingcenter is located at the above-mentioned L_(0′) not shown in thedrawing), a welding operation is performed as will be describedhereinafter.

FIG. 19 is a diagram showing a relationship between the weaving positionof the welding wire and the welding voltage generated in the weldingwire under such welding conditions that maximize the forcing-out of amelt to the back side of a groove by the welding apparatus shown in FIG.16.

In this case, in a range that the welding wire 6 moves from theabove-mentioned, unillustrated center L_(0′) toward the second basematerial 2, reaches the position L_(2′) and then returns to the centerL_(0′), the voltage waveform shows the same locus as the voltageindicated by the above-described, dashed curve in FIG. 18. When thewelding wire 6 moves past the center L_(0′) and is oscillated toward thefirst base material 1, however, an excessively large quantity of heatenters an end portion of the first base material 1 of small thermalcapacity, said end portion being located on the side of the singlegroove face 1 b, at a certain position beyond the center L_(0′) so thatpunching-through of an arc to the back side of the groove takes place.An arc is then formed between the tip of the welding wire 6 and thesecond base material 2, resulting in a sudden increase in the distancetherebetween.

As a result, the voltage which has varied following the same locus asthe dashed curve in FIG. 18 leaves the locus and increases suddenly. Thevoltage then rises further little by little because the distance betweenthe tip of the welding wire 6 and the second base material 2 graduallywidens until the position L_(1′) is reached. When the welding wirebegins to return from the position L_(1′) the voltage also begins todrop gradually. Concurrently with elimination of a punching-through as aresult of a decrease in the input of heat to the end portion of thefirst base material 1, the voltage returns onto the above-mentionedlocus of the dashed curve in FIG. 18, and on and along the locus,eventually reaches the position L_(0′).

As has been described above, the time interval during which the voltagesuddenly rises when the welding wire 6 is located on the side of thefirst base material 1 relative to the position L_(0′) has a correlationwith the amount of a bead to be formed on the back side of the groove.Like the above-mentioned, dashed curve in FIG. 18, the formation of abead is minimized if the time interval during which the voltage suddenlyrises does not exist. It has also been found that, if this time intervalis too long, on the other hand, punching-through of the arc takes placeexcessively to separate the first base material 1 and the bead B4 fromeach other and hence, no good welding results are available.

It is, therefore, necessary to control the duration of this timeinterval in accordance with a desired amount of a bead to be formed.Especially when there is a time interval during which the voltage risessuddenly, it is necessary to control its duration.

FIG. 20 and FIG. 21 are flow charts illustrating a control procedure forthe weaving position of the welding wire in the welding apparatus shownin FIG. 16. This control is performed by the robot controller 4. In thiscontrol, the voltage is firstly monitored to check whether or not thevoltage is at the maximum point V₁. Upon detection of the maximum pointV₁ (a voltage corresponding to the position P₁), it is determined fromthree-dimensional coordinate data of the robot main body 3 and thedirection of an operation of the welding torch 5 whether the currentposition of the welding torch 5 is on the side of the first basematerial 1 or on the side of the second base material 2 relative to theweaving center (step S2). The routine returns to step S1 if the currentposition of the welding torch is on the side of the second base material2, or awaits an elapse of a first predetermined time Δt1 if the currentposition of the welding torch is on the side of the groove (step S3).When the first predetermined time Δt1 has elapsed, it is determinedwhether or not the voltage has arisen above a predetermined threshold V2(step S4). If “NO”, it is determined whether or not a secondpredetermined time Δt2 has elapsed (step S5). If “YES”, step S13 isperformed as will be described subsequently herein. If the secondpredetermined time Δt2 is not determined to have elapsed, the routinereturns to step S4. If the voltage is determined to have arisen abovethe threshold V2 in step S4, a current time t3 is stored in the inputunit 4A (step S6). Subsequent to the storage of the time t3, it isdetermined whether or not the voltage has fallen below the threshold V2(step S7). If “NO”, it is determined whether or not the secondpredetermined time Δt2 has elapsed (step S8). If “YES”, step S12 isperformed as will be described subsequently herein. If the secondpredetermined time Δt2 is not determined to have elapsed, the routinereturns to step S7. If the voltage is determined to have fallen belowthe threshold V2 in step S7, a current time t4 is stored (step S9).

Next, the routine awaits a lapse of the second predetermined time Δt2(step S1). If the second predetermined time Δt2 is determined to haveelapsed, the difference between the time t4 and the time t3 (t4−t3) iscompared with a target time Δt0 that permits adequate melting of the endportion of the first base material 1 without being punched through (stepS11). If the former is longer than the latter, the amount ofpunching-through is excessive so that the weaving center is correctedtoward the second base material 2 (step S12). If they are equal to eachother, the weaving center is left unchanged. If the former is shorterthan the latter, the amount of punching-through is insufficient so thatthe weaving center is corrected toward the first base material 1 (stepS13).

If the second predetermined time Δt2 is determined to have elapsedwithout the voltage arising above the threshold V2 in step S5, on theother hand, the amount of punching-through is insufficient so that theweaving center is corrected toward the first base material 1 (step S13).If the second predetermined time Δt2 is determined to have elapsedwithout the voltage falling below the threshold V2 in step S8, on theother hand, the amount of punching-through is excessive so that theweaving center is corrected toward the second base material 2 (stepS12). As an alternative, these cases may be taken as an indication of apoor bead, and a command may be sent to the robot controller 4 to stopthe welding.

The amount of the correction of the weaving center in step S12 or stepS13 is suitably changed depending on the magnitude of the difference instep 11 and also depending on whether the correction is performed afterstep S5 or after step S8, and a command is outputted to the robotcontroller 4. In addition to the correction of the weaving center,welding conditions such as welding current and speed may also bechanged.

Further, the threshold V2 and target time Δt0 and the first and secondpredetermined times Δt1, Δt2 are changed depending on the weldingconditions, the groove shape, the target amount of a bead to be formed,etc.

As has been described above, the weaving center can be automaticallycorrected based on changes in actual voltage as monitored when thewelding wire 6 is located on the side of the first base material 1. Evenif the first and second base materials 1,2 are caused to warp upward ordownward during welding such that the aimed point becomes offset fromthe preset point, the welding can be still continued while correctingthe offset. A bead in the form of a fillet weld can, therefore, becaused to deposit efficiently with higher accuracy on the opposite sideof the groove by simply performing arc welding from the side of thegroove.

If the groove shifts or deforms in the direction of its distance to thetip of the welding wire 6, the welding wire is also controlled to movealong a weld line.

In such a case, time is clocked from a return of the welding wire 6 tothe contact position P₁ subsequent to its oscillation toward the grooveof the first base material 1 by weaving until a return of the weldingwire 6 to the contact position P₁ subsequent to its oscillation towardthe second base material 2 (see FIG. 19 described above). During thistime, actual voltages fed to the welding wire 6 are measured, and anactual average voltage during a single reciprocation of weaving from thecontact point P₁ as the base point toward and from the second basematerial 2 is computed. Now assume that in FIG. 19, V₀ is a presetaverage voltage level. When the actual average voltage rises above apredetermined upper limit threshold V_(OU), the distance between thewelding wire 6 and the welded portion in the groove is taken to begreater than a predetermined, preset value and the welding wire 6 ismoved toward the groove (in FIG. 17, in the horizontal direction towardthe contact position P₁). When the above-described actual averagevoltage conversely falls below a lower limit threshold V_(OL), thedistance between the welding wire 6 and the groove is taken to besmaller than the predetermined, preset value and the welding wire 6 ismoved away from the groove (from the side of the contact position P₁ inFIG. 17) in the horizontal direction.

When weaving is performed as described above, stable leg lengths as muchas 7 to 5 mm in the vertical direction (the solid line which connectssquare dots) and 4 to 3 mm in the horizontal direction (the solid linewhich connects triangle dots) can be obtained in a wide range that thedistance between the contact position P₁ and the aimed point P₂ rangesfrom 0.5 mm to 5 mm, as illustrated in FIG. 24. In other words, suchweaving makes it possible to provide the offset of the aimed point witha greater tolerance.

In the foregoing, the description was made about the case in whichvariations in voltage were monitored. As an alternative, variations incurrent may be monitored. In such a case, increases or decreases takeplace in a form reversed to those in the case of voltage. As the weldingcurrent, a current of pulse waveform, a sunisoidal current or the like,which has high directivity, can be used instead of a direct current,although use of a high-directivity current such as a current of pulsewaveform is preferred.

6. Sixth Embodiment

FIG. 22 is the diagram showing the construction of the welding apparatusaccording to the sixth embodiment of the present invention. In thisembodiment, elements equivalent to the corresponding elements in theabove-described fifth embodiment shown in FIG. 16 are designated by likereference signs, and overlapping descriptions are omitted.

The welding apparatus according to the sixth embodiment is constructedsuch that a pulse current is superimposed on a welding current. To thewelding apparatus depicted in FIG. 16, a pulse waveform control device19 is added in parallel with the voltage control device 13 and currentcontrol device 15 at a stage preceding an output control device 22′. Ata stage preceding the pulse waveform control device 19, a peak voltagesetting device 16 for setting a peak voltage for the pulse current, abase voltage setting device 17 for setting a base voltage for the pulsecurrent and a pulse duration setting device 18 for setting a pulseduration for the pulse current are arranged in parallel with oneanother, and the real time of the pulse duration is inputted from apower diagnosis unit 23′. To the pulse waveform control device 19, thepeak voltage, base voltage and pulse duration are inputted from the peakvoltage setting device 16, base voltage setting device 17 and pulseduration setting device 18, respectively. Based on these inputs, adesired pulse waveform is produced as a basis.

Based on control signals inputted from the voltage control device 13,current control device 15 and pulse waveform control device 19, theoutput control device 22′ controls welding electric power to beoutputted from the welding power source 9. The power diagnosis unit 23′is composed of an input unit 23A′, a comparison unit 23B′, an outputunit 23C, and the like. The input unit 23A′ sets a first preset voltagehigher than the average voltage set by the average voltage settingdevice 12, a second preset voltage lower than the average voltage set bythe average voltage setting device 12, and a preset current higher thanthe average current set by the average current setting device 14. Thecomparison unit 23B′ compares an actual voltage, which is inputted fromthe voltage detector 10, with the first and second present voltages andoutputs a positional control signal, which will be describedsubsequently herein, to the robot controller 4, and also compares anactual current, which is inputted from the current detector 11, with thepreset current and outputs a positional control signal to the robotcontroller 4. The comparison unit 23B′ is also equipped with a functionto determine, in addition to an actual average voltage and an actualaverage current, the actual peak current (or voltage) of the pulsecurrent, the actual base current (or voltage) of the pulse current andthe real time (width) of each pulse on the basis of detection valuesdetected by the voltage detector 10 and current detector 11,respectively. From the output unit 23C′, the actual average voltage andthe actual average current are outputted to the voltage control device13 and the current control device 15, respectively, while the actualpeak current, the actual base current and the real time of the pulseduration are outputted to the pulse waveform control device 19. Like thefifth embodiment, the welding apparatus is equipped with a computer orthe like, which controls all of the above-described individual controldevices, robot and the like.

Welding which makes use of the welding apparatus constructed asdescribed above is performed as will be described hereinafter.

Reference is had to FIG. 22. When from the peak voltage setting device16, base voltage setting device 17 and pulse duration setting device 18,their respective preset values are inputted to the pulse waveformcontrol device 19, a pulse waveform is produced at the pulse waveformcontrol device 19. Its waveform control signal is outputted to theoutput control device 22′. Based on an average voltage control signalfrom the voltage control device 13, an average current control signalfrom the current control device 15 and the pulse waveform control signalfrom the pulse waveform control device 19, the output control device 22′controls the welding power source 9 such that electric power of thedesired waveform is supplied from the welding power source 9. Dependingon the characteristics of the power source 9 employed for the welding,the pulse waveform is set based on one or both of current and voltage.

FIG. 23 is, as already referred to in brief, the waveform diagram of thepulse current for the welding apparatus according to the fifthembodiment shown in FIG. 22.

FIG. 23 shows a peak current A_(p), a base current A_(b), and a pulsewidth, namely, pulse duration T_(p). A_(a) indicates an average current.This average current A_(a) is set by the above-described, averagecurrent setting device 14. Based on these preset values A_(p), A_(b),T_(p) and A_(a), the width, namely, time T_(b) of the base current ofpulses is determined by the above-described output control device 22′,and a waveform in the form of a direct current with a pulse waveformsuperimposed thereon is supplied as an output control signal to thewelding power source 9.

More specifically, with a waveform indicated by a solid line in FIG. 23,the peak current A_(p), base current A_(b) and pulse duration T_(p) aregiven, for example, as 400 A, 200 A and 1/50 sec, respectively. Further,a value determined as the width, namely, duration T_(b) of the basecurrent on the basis of an average current A_(a) of 300 A given from theaverage current setting device 14 (in this case, T_(b)=T_(p)= 1/50 sec)is indicated.

When a pulse current obtained by super imposing a pulse-like current ona direct current is used as a welding current as described above, thedirectivity of an arc is enhanced compared with use of a currentconsisting of a direct current alone, thereby making it possible toproduce the arc more accurately at a point aimed by the welding wire 6and hence to perform more stable arc welding of a groove.

On the other hand, a waveform indicated by a double dashed line in FIG.23 is a pulse waveform obtained, for example, when the peak current wasraised further by 100 A to A_(p′) (=500 A), the pulse duration wasshortened to ½ of that in the case of the solid line, and the averagecurrent A_(a) and base current A_(b) were set at 300 A and 200 A,respectively, as in the case of the solid line.

In this case, the base current A_(b) (=200 A) and average current A_(a)(=300 A) were set at the same levels as in the case of the waveformindicated by the solid line. In the case of the waveform indicated bythe solid line, the cycle of pulses is (T_(p)+T_(b)). In the case of thewaveform indicated by the double dashed line, on the other hand, thecycle is therefore shortened to ((T_(p)×½)+T_(b)). Expressing this interms of duty, the duty in the case of the waveform indicated by thesolid line is expressed by:T _(p)/(T _(p) +T _(b))=( 1/50)/(1/50+ 1/50)=½whereas the duty in the case of the waveform indicated by the doubledashed line is expressed by:T _(p′)/(T _(p′) +T _(b′))=( 1/50×½)/(( 1/50×½)+ 1/50)=⅓

A waveform indicated by a dashed line in FIG. 23 is a pulse waveformobtained when relative to the waveform indicated by the solid line, thepeak current A_(p), base current A_(b) and average current A_(a) wereleft unchanged at 400 A, 200 A and 300 A, respectively, as in the caseof the solid line and the pulse duration T_(p″) was shortened to ½ ofthat in the case of the waveform indicated by the solid line. In thiscase, the base current width T_(b″) becomes equal to T_(p″), and theduty is ½ as in the case of the waveform indicated by the solid line.

In FIG. 23, some examples of pulse waveforms are shown as describedabove. An arc is provided with improved directivity when the duty of apulse waveform is rendered smaller. However, the average current A_(a),the peak current A_(p) and base current A_(b) of pulses, and the like inwelding are correlated to various welding conditions and the like. Fromthe standpoints of the transfer of globules by a welding arc, thestability of the arc, and the like, practical values of the averagecurrent A_(a), base current A_(b) and peak current A_(p) in thisembodiment can be around 300 A, not higher than 300 A (including anegative ampere), and 350 to 500 A or so, respectively.

As has been described above, the welding apparatus according to thisembodiment, in addition to the control in the welding apparatusaccording to the fifth embodiment described above with reference to FIG.16, uses a pulse current as a welding current and controls the pulsecurrent such that the pulse current becomes equal to a preset value.This has made it possible to increase the directivity of an arc and tocontrol the arc to the aimed point more accurately. As a consequence,stable welding can be performed on the groove without leaving any partundeposited by simply welding from the side of the groove while allowinga bead to deposit in the form of a fillet weld on the back side 1 c ofthe groove.

Although not illustrated in any drawing, the peak voltage setting device16, base voltage setting device 17, pulse duration setting device 18 andpulse waveform control device 19 in the welding apparatus according tothis embodiment can be replaced by a sunisoidal current setting device.Because a sunisoidal current can be used as a welding current in thiscase, an arc can be provided with improved directivity similarly to thewelding apparatus according to the sixth embodiment. As a result,similar welding can be performed as the welding apparatus according tothe sixth embodiment.

As has been described above, the embodiments of the welding methodaccording to the present invention and the embodiments of the weldingapparatus according to the present invention have made it possible toperform the formation of an auxiliary bead without using any backingmaterial or the like by one-side welding to the area of contact betweenthe first base material 1 and the second base material 2 where a groovesuch as a single bevel groove or a single J groove is formed by aone-side groove wall, although such one-side welding has heretofore beeninfeasible unless a backing material or a bead, which does notcontribute to the joining, is additionally applied. As a consequence, itis possible to significantly reduce the fabrication cost of abox-shaped, welded structure which has required a substantial time forwelding work inside the structure.

In a structure inside which welding has heretofore been impossible dueto a difficulty in inserting the welding torch 5, a leg length reachesboth of the side of the groove and the back side of the groove, therebybringing about significant advantageous effects in that the resultingjoint can be provided with substantially improved strength and thestrength of the joint can be retained without unnecessarily increasingthe thicknesses of two base materials to be brought into abutment.

In connection with a butt-welded joint, the present invention requireswelding work only from one side even if the butt-welded joint is of sucha welded structure that has heretofore required to also perform weldingon the back side of the groove. The present invention, therefore, makesit possible to efficiently decrease the number of welding steps. Owingto these advantageous effects, it is also possible to achievediversification and to improve efficiency as to the designing of awelded structure.

INDUSTRIAL APPLICABILITY

As has been described above, the welding method according to the presentinvention makes it possible to achieve welding in a groove and also tostably deposit a bead in the form of a fillet weld on the back side ofthe groove owing to a difference in thermal capacity between a firstbase material provided with the groove face and a second base materialhaving a flat surface and fusion of a welding wire. Describedspecifically, a bead in the form of a fillet weld can also be formed bycausing a greater portion of an arc to generate on the side of thesecond material the thermal capacity of which is greater; causing thefirst base material, the thermal capacity of which is smaller, to fuseto such an extent that an end portion of the first base material, saidend portion being located on the side of a single groove face, is notpunched through; and forcing out a melt of the welding wire to the backside of the groove while filling up the groove owing to melting of thewelding wire. As a result, no work is needed for the arrangement of anauxiliary bead so that the workability can be improved significantly.

In addition, according to welded joints and welded structures of thepresent invention, the fabrication cost is low and further, thefabrication time can be shortened. It is, therefore, possible to improvethe productivity of products in which such welded joints and/or weldedstructures are incorporated.

According to the welding apparatus of the present invention, theposition of the welding wire can be controlled with high accuracy. Itis, therefore, possible to provide welded joints, structures of closedcross-sections and the like, each of which has been fabricated such thatone or more beads in the form of fillet weld or welds are depositedinside by arranging a single groove face at at least one location on anouter side of a base material and then performing welding to the groovefrom the outside. Accordingly, their productivity can be improvedsubstantially.

Moreover, the tolerance of an offset from an aimed point can be enlargedby weaving the welding wire. As a result, welding can be performed withhigh accuracy and high efficiency, thereby significantly improving thewelding workability.

1. A welding apparatus for butt welding a first base material and asecond base material with each other, comprising: a welding wire to beintroduced into a groove formed at an area of contact between said firstbase material and said second material, a control device for controllinga position of said welding wire, a welding power source for feedingwelding electric power to said area of contact, and control means foroutputting a command to said control device such that said welding wireis moved toward said second base material when an actual voltage fedfrom said welding power source to said area of contact has exceeded afirst preset voltage level set in advance and said welding wire is movedtoward said first base material when an actual current fed from saidwelding power source to said area of contact has exceeded a presetcurrent level set in advance or said actual voltage has fallen below asecond preset voltage level set in advance.
 2. A welding apparatus forbutt welding a first base material and a second base material with eachother, comprising: a welding wire to be introduced into a groove formedat an area of contact between said first base material and said secondmaterial, a control device for controlling a position of said weldingwire, a welding power source for feeding welding electric power to saidarea of contact, and control means for outputting a command to saidcontrol device such that said welding wire is moved toward said secondbase material when an actual voltage fed from said welding power sourceto said area of contact has exceeded a first preset voltage level set inadvance and said welding wire is moved toward said first base materialwhen an actual current fed from said welding power source to said areaof contact has exceeded a preset current level set in advance or saidactual voltage has fallen below a second preset voltage level set inadvance and also for comparing said actual current and voltage with apreset average current level and preset average voltage level set inadvance, respectively, and outputting a current control signal andvoltage control signal to said welding power source such that theseactual current and voltage are brought into conformity with said presetcurrent and voltage levels set in advance.
 3. A welding apparatus forbutt welding a first base material and a second base material with eachother, comprising: a welding wire, a welding torch for holding saidwelding wire in place, feeding means for feeding said welding wire tosaid welding torch, a control unit provided with a position controldevice for positionally controlling said welding wire in directions ofthree orthogonal axes, a welding power source for feeding weldingelectric power to an area of contact between said first base materialand said second base material, an average voltage setting device forsetting an average voltage level for said welding, an average currentsetting device for setting an average current level for said welding, avoltage detector and current detector for detecting an actual weldingvoltage and actual welding current to form, by said welding wirepositioned facing on a groove formed by a single groove face arranged onsaid first base material and a flat surface of said second basematerial, a bead in a form of a fillet weld on a back side of saidgroove, a power diagnosis unit for being inputted with said actualvoltage detected by said voltage detector and said actual currentdetected by said current detector and outputting a command to saidposition control device such that said welding wire is moved toward saidsecond base material when said actual voltage has exceeded a firstpreset voltage level set in advance and said welding wire is movedtoward said first base material when said actual current detected bysaid current detector has exceeded a preset current level set in advanceor said actual voltage detected by said voltage detector has fallenbelow a second preset voltage level set in advance and also foroutputting said actual voltage and outputting said actual current, saidcurrent control device for comparing said average current level inputtedfrom said average current setting device with said actual currentinputted from said power diagnosis unit and outputting a current controlsignal such that this actual current is brought into correspondence withsaid preset current level set in advance, a voltage control device forcomparing said average voltage level inputted from said average voltagesetting device with said actual voltage inputted from said powerdiagnosis unit and outputting a voltage control signal such that thisactual voltage is brought into conformity with said preset voltage levelset in advance, and said output control device for being inputted withsaid current control signal outputted from said current control deviceand said voltage control signal outputted from said voltage controldevice, and based on said current control signal and voltage controlsignal, outputting a power source control signal to said welding powersource to control an output of said power source.
 4. A welding apparatusaccording to claim 3, wherein said welding apparatus is provided with: apeak voltage setting device for setting a peak voltage for a pulsevoltage, a base voltage setting device for setting a base voltage, apulse duration setting device for setting a pulse duration, and a pulsewaveform control device for being inputted with said preset peakvoltage, preset base voltage level and preset pulse duration from saidpeak voltage setting device, base voltage setting device and pulseduration setting device, respectively, comparing these preset valueswith an actual peak voltage, actual base voltage and actual pulseduration, respectively, and outputting a waveform control signal to saidoutput control device, said power diagnosis unit comprises means fordetermining an actual peak voltage, actual base voltage and actual pulseduration on a basis of said actual voltage detected by said voltagedetector and said actual current detected by said current detector, andoutputting the thus-determined actual peak voltage, actual base voltageand actual pulse duration to said pulse waveform control device, andsaid output control device comprises means for being inputted with saidwaveform control signal outputted from said pulse waveform controldevice and outputting a power source control signal, which controls anoutput of said power source, to said welding power source on a basis ofsaid voltage control signal inputted from said voltage control deviceand said current control signal inputted from said current controldevice.
 5. A welding apparatus according to claim 3, wherein: said pulsewaveform control device comprises sinusoidal current forming means forconverting a welding current into a sinusoidal current, comparing apreset sinusoidal waveform, which has been set in advance, with anactual sinusoidal waveform and outputting a waveform control signal tosaid output control device, said power diagnosis unit comprises meansfor determining an actual current waveform on a basis of said actualvoltage detected by said voltage detector and said actual currentdetected by said current detector, and outputting the thus-determinedactual current waveform to said sinusoidal current forming means, andsaid output control device comprises means for outputting a power sourcecontrol signal, which controls an output of said power source, to saidwelding power source on a basis of said waveform control signal inputtedfrom said sinusoidal current forming means, said voltage control signalinputted from said voltage control device and said current controlsignal inputted from said current control device.
 6. A welding apparatusfor butt welding a first base material and a second base material witheach other, comprising: a welding wire to be introduced through awelding torch into a groove formed by bringing said first base material,on which a root face and a single groove face have been formed, intocontact with said second material having a flat surface, a controldevice for controlling a position of said welding wire, a welding powersource for feeding welding electric power to said area of contact, avoltage detector for detecting an actual voltage to be fed from saidwelding power source to said area of contact, a clock device fordetecting a time, at which an arc from said welding wire passes througha position of contact between an end portion of said single groove faceand said flat surface, and clocking a time after said arc passes throughsaid position of contact until said arc moves toward said first basematerial and returns back to said predetermined position, memory meansfor storing a change in welding voltage during said clocking time bysaid voltage detector and said clock device, and wire position controlmeans for continuing preceding weaving control when a time (t4−t3)—t3being a time at which an actual voltage begins to exceed a presetvoltage level set in advance and t4 being a time at which said actualvoltage falls below said preset voltage level, both while clocking asecond predetermined time Ate subsequent to an elapse of a firstpredetermined time At, from a time point at which said welding wirepassed through said position of contact during said clocking time—fallswithin a target time range in which adequate fusion takes place withoutpunching through said first base material, moving a center axis ofweaving of said welding wire toward said second base material when saidtime (t4−t3) exceeds said target time, and moving said center axis ofweaving toward said first base material when said time (t4−t3) fallsbelow said target time.
 7. A welding apparatus for butt welding a firstbase material and a second base material with each other, comprising: awelding wire to be introduced through a welding torch into a grooveformed by bringing said first base material, on which a root face and asingle groove face have been formed, into contact with said secondmaterial having a flat surface, a control device for controlling aposition of said welding wire, a welding power source for feedingwelding electric power to said area of contact, a current detector fordetecting an actual current to be fed from said welding power source tosaid area of contact, a clock device for detecting a time, at which anarc from said welding wire passes through a position of contact betweenan end portion of said single groove face and said flat surface, andclocking a time after said arc passes through said position of contactuntil said arc moves toward said first base material and returns back tosaid predetermined position, memory means for storing a change inwelding current during said clocking time by said current detector andsaid clock device, and wire position control means for continuingpreceding weaving control when a time (t4—t3)−t3 being a time at whichan actual current begins to fall below a preset current level set inadvance and t4 being a time at which said actual current exceeds saidpreset voltage level, both while clocking a second predetermined timeAte subsequent to an elapse of a first predetermined time At, from atime point at which said welding wire passed through said position ofcontact during said clocking time—falls within a target time range inwhich adequate fusion takes place without punching through said firstbase material, moving a center axis of weaving of said welding wiretoward said second base material when said time (t4−t3) exceeds saidtarget time, and moving said center axis of weaving toward said firstbase material when said time (t4−t3) falls below said target time.
 8. Awelding apparatus for butt welding a first base material and a secondbase material with each other, comprising: a welding wire to beintroduced through a welding torch into a groove formed by bringing saidfirst base material, on which a root face and a single groove face havebeen formed, into contact with said second material having a flatsurface, a control device for controlling a position of said weldingwire, a welding power source for feeding welding electric power to saidarea of contact, a voltage detector for detecting an actual voltage tobe fed from said welding power source to said area of contact, a clockdevice for detecting a time, at which an arc from said welding wirepasses through a position of contact between an end portion of saidsingle groove face and said flat surface, and clocking a time after saidarc passes through said position of contact until said arc moves towardsaid first base material and returns back to said predeterminedposition, memory means for storing a change in welding voltage duringsaid clocking time by said voltage detector and said clock device, andwire tip position control means for moving a tip of said welding wireaway from said position of contact when an actual average voltage duringsaid clocking time falls below a preset first voltage level, moving saidtip of said welding wire toward said position of contact when saidactual average voltage exceeds a preset second voltage level, andmaintaining said tip of said welding wire at a preceding position whensaid actual average voltage falls between said preset first voltagelevel and said preset second voltage level.
 9. A welding apparatus forbutt welding a first base material and a second base material with eachother, comprising: a welding wire to be introduced through a weldingtorch into a groove formed by bringing said first base material, onwhich a root face and a single groove face have been formed, intocontact with said second material having a flat surface, a controldevice for controlling a position of said welding wire, a welding powersource for feeding welding electric power to said area of contact, acurrent detector for detecting an actual current to be fed from saidwelding power source to said area of contact, a clock device fordetecting a time, at which an arc from said welding wire passes througha position of contact between an end portion of said single groove faceand said flat surface, and clocking a time after said arc passes throughsaid position of contact until said arc moves toward said first basematerial and returns back to said predetermined position, memory meansfor storing a change in welding current during said clocking time bysaid current detector and said clock device, and wire tip positioncontrol means for moving a tip of said welding wire away from saidposition of contact when an actual average current during said clockingtime exceeds a preset first current level, moving said tip of saidwelding wire toward said position of contact when said actual averagecurrent falls below a preset second current level, and maintaining saidtip of said welding wire at a preceding position when said actualaverage current falls between said preset first current level and saidpreset second current level.
 10. A welding method for butt welding afirst base material and a second base material with each other, saidfirst base material having an abutting end portion with a groove faceand a root face formed on a side thereof and on a free end thereof,respectively, and said second base material having a flat surface atwhich said first base material is to be brought into contact with saidsecond base material, which comprises: bringing said root face of saidfirst base material into contact with said flat surface of said secondbase material, arranging a welding wire to face at a predeterminedinclination relative to said flat surface of said second base materialsuch that a center axis of an arc from said welding wire is to bedirected toward a position of contact between an end portion of saidgroove face of said first base material and said flat surface of saidsecond base material or a position adjacent and not farther than saidposition of contact, and then, in a course of performing arc welding,inputting less heat in said first base material than in said second basematerial such that said abutting end portion of said first base materialis caused to fuse to a back side thereof without a bum-through whilecausing said flat surface of said second base material to fuse, therebyto form a molten pool with melts of said first base material, secondbase material and welding wire, forcing out said molten pool to saidback side of said abutting end portion of said first base material suchthat said molten pool is formed extending integrally from an inside ofsaid groove to said back side of said abutting end portion of said firstbase material, and allowing said molten pool to resolidify such that abead is formed in a form of a fillet weld on said back side of saidabutting end portion of said first base material.
 11. A welding methodaccording to claim 10, wherein said welding wire is caused to weave witha predetermined oscillation width within said groove while maintainingsaid predetermined inclination.
 12. A welding method according to claim10, wherein said welding wire is caused to weave with a predeterminedoscillation width with a center of weaving set at a predetermined pointon said predetermined inclination within said groove.
 13. A weldingmethod according to claim 11 or 12, wherein: while said welding wire isweaving, a change in welding voltage or welding current during a timeafter said arc moves past said position of contact until said arc movestoward said first base material and returns back to said position ofcontact is detected based on a time at which said arc passes throughsaid position of contact, and said welding wire is moved in a directionof a width of said groove on a basis of the thus-detected change suchthat said center of said weaving always remains at an appropriateposition relative to said groove.
 14. A welding method according toclaim 11 or 12, wherein: while said welding wire is weaving, a change inwelding voltage or welding current during a time after said arc movespast said position of contact until said arc moves toward said firstbase material and returns back to said position of contact is detectedbased on a time at which said arc passes through said position ofcontact, and a tip of said welding wire is moved toward or away fromsaid position of contact on a basis of the thus-detected change suchthat said center of weaving always remains at an appropriate positionrelative to said groove.
 15. A welding method according to claim 10wherein a current for generating said arc is a direct current.
 16. Awelding method according to claim 10 wherein a current for generatingsaid arc is a current obtained by superimposing a direct current and apulse current on each other.
 17. A welding method according to claim 10wherein a current for generating said arc is a sinusoidal current.
 18. Awelded “T” joint with a first base material and a second base materialbutt welded with each other, said first base material having an abuttingend portion with a groove face and a root face formed on a side thereofand on a free end thereof, respectively, and said second base materialhaving a flat surface at which said first base material is to be broughtinto contact with said second base material, wherein said welded “T”joint has been fabricated by: bringing said root face of said first basematerial into contact with said flat surface of said second basematerial, arranging a welding wire to face at a predeterminedinclination relative to said flat surface of said second base materialsuch that a center axis of an arc from said welding wire is to bedirected toward a position of contact between an end portion of saidgroove face of said first base material and said flat surface of saidsecond base material or a position adjacent and not farther than saidposition of contact, and then, in a course of performing arc welding,inputting less heat in said first base material than in said second basematerial such that said abutting end portion of said first base materialis caused to fuse to a back side thereof without a bum-through whilecausing said flat surface of said second base material to fuse, therebyto form a molten pool with melts of said first base material, secondbase material and welding wire, forcing out said molten pool to saidback side of said abutting end portion of said first base material suchthat said molten pool is formed extending integrally from an inside ofsaid groove to said back side of said abutting end portion of said firstbase material, and allowing said molten pool to resolidify such that abead is formed in a form of a fillet weld on said back side of saidabutting end portion of said first base material.
 19. A butt-welded “T”joint of flat plates with a first base material and a second basematerial butt welded with each other, said first base material having anabutting end portion with a groove face and a root face formed on a sidethereof and on a free end thereof, respectively, and said second basematerial having a flat surface at which said first base material is tobe brought into contact with said second base material, wherein saidbutt-welded “T” joint has been fabricated by: bringing said root face ofsaid first base material into contact with said flat surface of saidsecond base material, arranging a welding wire to face at apredetermined inclination relative to said flat surface of said secondbase material such that a center axis of an arc from said welding wireis to be directed toward a position of contact between an end portion ofsaid groove face of said first base material and said flat surface ofsaid second base material or a position adjacent and not farther thansaid position of contact, and then, in a course of performing arcwelding, inputting less heat in said first base material than in saidsecond base material such that said abutting end portion of said firstbase material is caused to fuse to a back side thereof without abum-through while causing said flat surface of said second base materialto fuse, thereby to form a molten pool with melts of said first basematerial, second base material and welding wire, forcing out said moltenpool to said back side of said abutting end portion of said first basematerial such that said molten pool is formed extending integrally froman inside of said groove to said back side of said abutting end portionof said first base material, and allowing said molten pool to resolidifysuch that a bead is formed in a form of a fillet weld on said back sideof said abutting end portion of said first base material.
 20. Abox-shaped structure formed of a plurality of plates comprising a firstplate and a second plate butt-welded with each other, said first platehaving an abutting end portion with a groove face and a root face formedon a side thereof and on a free end thereof, respectively, and saidsecond plate having a flat surface at which said first plate is to bebrought into contact with said second plate, wherein said box-shapedstructure has been fabricated by: bringing said root face of said firstplate into contact with said flat surface of said second plate,arranging a welding wire to face at a predetermined inclination relativeto said flat surface of said second plate such that a center axis of anarc from said welding wire is to be directed toward a position ofcontact between an end portion of said groove face of said first plateand said flat surface of said second plate or a position adjacent andnot farther than said position of contact, and then, in a course ofperforming arc welding, inputting less heat in said first plate than insaid second plate such that said abutting end portion of said firstplate is caused to fuse to a back side thereof without a burn-throughwhile causing said flat surface of said second plate to fuse, thereby toform a molten pool with melts of said first plate, second plate andwelding wire, forcing out said molten pool to said back side of saidabutting end portion of said first plate such that said molten pool isformed extending integrally from an inside of said groove to said backside of said abutting end portion of said first plate, and allowing saidmolten pool to resolidify such that a bead is formed in a form of afillet weld on said back side of said abutting end portion of said firstplate.